Homogeneous Charge Combustion Ignition (HCCI) is an advanced form of internal engine combustion that offers important potential advantages in reduced emissions and higher fuel efficiency compared to conventional spark ignition (SI) combustion. However, practical utilization of HCCI for transportation requires overcoming significant technical barriers in stabilizing HCCI and controlling engine transitions between HCCI and SI. While SI combustion is likely to remain a basic feature of future engines, maximizing the range of speed and load at which HCCI is possible will be key to realizing their full potential. Increased HCCI implementation is a difficult challenge because HCCI is much more sensitive than SI to small changes in the initial in-cylinder charge conditions. In addition, uncontrolled HCCI can create unacceptable in-cylinder pressure rise rates that structurally damage the engine. Finally, realistic driving conditions require frequent transitions between HCCI and SI, which, without proper control, can result in severe upsets in engine performance and emissions.
The sensitivity of HCCI to small perturbations makes maximizing its operating limits and managing mode transitioning between SI and HCCI a difficult problem. However, there are good reasons to expect that these goals can be achieved in practical engines because the dominant instabilities in HCCI are deterministic, and thus predictable. The deterministic nature of HCCI instabilities have only been recently revealed in methodical experimental studies. Although the transition between SI and HCCI is very nonlinear, it exhibits very characteristic features of low-dimensional, deterministic bifurcation processes similar to those seen in other engineering processes. The fact that many of these other bifurcation processes have been successfully controlled by utilizing tools from the science of nonlinear dynamics suggests that there is hope for doing the same with HCCI.